fix: wasm with starlette issue (#6648)

Some of the refactors to `mpl` brought in starlette top-level which does
not work for work in wasm

---------

Co-authored-by: dylan <dylan@marimo.io>

Author: mscolnick

marimo/_mcp/server/lifespan.py

@@ -1,17 +1,19 @@
 # Copyright 2025 Marimo. All rights reserved.
 import contextlib
 from collections.abc import AsyncIterator
-
-from starlette.applications import Starlette
+from typing import TYPE_CHECKING
 
 from marimo._loggers import marimo_logger
 from marimo._mcp.server.main import setup_mcp_server
 
 LOGGER = marimo_logger()
 
+if TYPE_CHECKING:
+    from starlette.applications import Starlette
+
 
 @contextlib.asynccontextmanager
-async def mcp_server_lifespan(app: Starlette) -> AsyncIterator[None]:
+async def mcp_server_lifespan(app: "Starlette") -> AsyncIterator[None]:
     """Lifespan for MCP server functionality (exposing marimo as MCP server)."""
 
     try:

marimo/_mcp/server/main.py

@@ -9,7 +9,6 @@
 from typing import TYPE_CHECKING
 
 from mcp.server.fastmcp import FastMCP
-from starlette.routing import Mount
 
 from marimo._ai._tools.base import ToolContext
 from marimo._ai._tools.tools_registry import SUPPORTED_BACKEND_AND_MCP_TOOLS
@@ -34,6 +33,7 @@ def setup_mcp_server(app: "Starlette") -> "StreamableHTTPSessionManager":
     Returns:
         StreamableHTTPSessionManager: MCP session manager
     """
+    from starlette.routing import Mount
 
     mcp = FastMCP(
         "marimo-mcp-server",

marimo/_plugins/stateless/mpl/_mpl.py

@@ -17,8 +17,6 @@
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Optional, Union
 
-from starlette.responses import HTMLResponse, Response
-
 from marimo import _loggers
 from marimo._output.builder import h
 from marimo._output.formatting import as_html
@@ -42,6 +40,7 @@
     from matplotlib.figure import Figure, SubFigure
     from starlette.applications import Starlette
     from starlette.requests import Request
+    from starlette.responses import HTMLResponse, Response
     from starlette.websockets import WebSocket
 
 
@@ -222,10 +221,12 @@ def _template(fig_id: str, port: int) -> str:
     }
 
 
+# Toplevel for reuse in endpoints.
 async def mpl_js(request: Request) -> Response:
     from matplotlib.backends.backend_webagg_core import (
         FigureManagerWebAgg,
     )
+    from starlette.responses import Response
 
     del request
     return Response(
@@ -235,19 +236,23 @@ async def mpl_js(request: Request) -> Response:
 
 
 async def mpl_custom_css(request: Request) -> Response:
+    from starlette.responses import Response
+
     del request
     return Response(
         content=css_content,
         media_type="text/css",
     )
 
 
+# Over all application for handling figures on a per kernel basis
 def create_application() -> Starlette:
     import matplotlib as mpl
     from matplotlib.backends.backend_webagg_core import (
         FigureManagerWebAgg,
     )
     from starlette.applications import Starlette
+    from starlette.responses import HTMLResponse, Response
     from starlette.routing import Mount, Route, WebSocketRoute
     from starlette.staticfiles import StaticFiles
     from starlette.websockets import (

marimo/_server/api/endpoints/mpl.py

@@ -7,15 +7,12 @@
 from typing import TYPE_CHECKING, Any, Callable, Optional
 
 import websockets
-from starlette.responses import Response
-
-# import StaticFiles from starlette
-from starlette.staticfiles import StaticFiles
 
 if TYPE_CHECKING:
     from collections.abc import Awaitable
 
     from starlette.requests import Request
+    from starlette.responses import Response
     from starlette.websockets import WebSocket
 
 
@@ -39,6 +36,7 @@ def mpl_fallback_handler(
     Args:
         path_prefix: Prefix to add to path when calling _mpl_handler (default "")
     """
+    from starlette.responses import Response
 
     def decorator(
         func: Callable[[Request], Awaitable[Response]],
@@ -80,6 +78,7 @@ async def mpl_static(request: Request) -> Response:
     from matplotlib.backends.backend_webagg_core import (
         FigureManagerWebAgg,
     )
+    from starlette.staticfiles import StaticFiles
 
     static_app = StaticFiles(
         directory=FigureManagerWebAgg.get_static_file_path()  # type: ignore[no-untyped-call]
@@ -93,6 +92,7 @@ async def mpl_images(request: Request) -> Response:
     """Fallback for image files from matplotlib."""
     path = request.path_params["path"]
     import matplotlib as mpl
+    from starlette.staticfiles import StaticFiles
 
     static_app = StaticFiles(directory=Path(mpl.get_data_path(), "images"))
     return await static_app.get_response(path, request.scope)
@@ -130,6 +130,8 @@ async def _mpl_handler(
     Returns:
         Response from the matplotlib server or error response
     """
+    from starlette.responses import Response
+
     # Proxy to matplotlib server
     # Determine the target port
     port = figure_endpoints.get(figurenum, None)